1. Field of the Invention
The invention relates to a twist drill having a sintered cemented carbide body, and like tools, and the use thereof.
2. Background Information
A twist drill, and the like tools, having sintered cemented carbide bodies (cermets) of this type are described in International Patent Applications published as WO 99/10549, WO 99/10550, WO 99/10551, WO 99/10552 and WO 99/10553 of the Assignee herein. The aforementioned International Patent Applications furthermore describe the use of these sintered cemented carbide bodies as cutting inserts and cutting bits and for manufacturing drills and cemented carbide tools and tool inserts of all kinds. The entire content of said international patent applications hereby is expressly incorporated herein by reference.
Thus, there is further known from U.S. Pat. No. 5,992,546 issued to Heinrich et al. on Nov. 30, 1999, corresponding to International Patent Application No. WO 99/10552, an elongate rotary tool for machining materials, the rotary tool comprising an elongate body at a first end, a shank at a second and opposite end, the elongate body and the shank sharing a common axis, at least one face on the elongate body at an end opposite the shank, wherein the at least one face defines a corresponding flute extending along the elongate body toward the shank, at least one flank on an end of the elongate body at an end opposite the shank, and a cutting edge at a juncture of the at least one face and the at least one flank, wherein the at least one flank, the at least one face, and the cutting edge at the juncture thereof of the elongate rotary tool comprise a cermet comprising at least one hard component and a binder.
There is also known from U.S. Pat. No. 6,010,283 issued to Heinrich et al. on Jan. 4, 2000, corresponding to International Patent Application No. WO 99/10553, a cutting tool for chip forming machining of workpiece materials, the cutting tool comprising a rake face over which chips formed during the chip forming machining of workpiece materials flow, a flank face, and a cutting edge, for cutting into the workpiece materials to form the chips, formed at a junction of the rake face and the flank face, wherein at least the rake face, the flank face and the cutting edge of the cutting tool comprise a cermet comprising at least one hard component and a binder.
U.S. Pat. No. 6,022,175 issued to Heinrich et al. on Feb. 8, 2000, which corresponds to International Patent Application No. WO 99/10550, refers to a rotary tool comprising an elongate tool body having an axially forward end and an axially rearward end, a hard insert affixed to the tool body at the axially forward end thereof, and the hard insert comprising a WC-cermet comprising tungsten carbide and a binder.
There is also known from U.S. Pat. No. 6,170,917 issued to Heinrich et al. on Jan. 9, 2001, corresponding to International Patent Application No. WO 99/99/10551, a pick-style tool comprising an elongate tool body having an axially forward end and an axially rearward end, a hard insert affixed to the tool body at the axially forward end thereof, and the hard insert comprising a cermet comprising tungsten carbide and a binder.
There is also known from U.S. Pat. No. 5,788,427 issued to Zitzlaff et al. on Aug. 4, 1998, an indexable insert having two parallel cutting edges on opposite sides of an indexable insert body in the form of a rectangular block. In the intermediately placed top surface descending toward the center line thereof, there is a chipbreaking structure comprising alternating projections and recesses. These projections and recesses constitute a row, centered on the center line, of spherical-like chipbreaking bodies, between which concave chip guiding surfaces are formed. During metalcutting operations, this provides an even flow of chips with the formation of short chips which are free of grooves and tears along the edges.
Further, there is known from U.S. Pat. No. 5,967,706 issued to Hughes, Jr. on Oct. 19, 1999, a high speed milling cutter using a wedge to secure an insert within a pocket of the milling cutter wherein the wedge is tapered in both the axial direction and the radial direction. A screw urges the wedge within a tapered cavity to press the insert within the pocket along the axial wedge angle while rotation of the cutter creates centrifugal forces urging the wedge radially outward, thereby forcing the wedge against the radial wedge surface to further compress the insert within the pocket. The insert pocket may be extended to radially encompass the insert, thereby providing additional support against centrifugal forces for the insert.
There is also known from U.S. Pat. No. 6,145,606 issued to Haga on Nov. 14, 2000, a cutting insert which comprises a pair of top surfaces which intersect to form a chisel edge, and a pair of concave surfaces wherein each one of the concave surfaces is adjacent to and intersects its corresponding one of the top surfaces. The cutting insert further includes a pair of end surfaces and a pair of arcuate surfaces. One of the arcuate surfaces intersects the one top surface and further intersects the one end surface whereby the one arcuate surface joins the one top surface and the one end surface. The other of the arcuate surfaces intersects the other top surface and further intersects the other end surface whereby the other arcuate surface joins the other top surface and the other end surface.
It is known from German Patent No. 32 11 047 and from its corresponding U.S. Pat. No. 34,180 that in the case of cemented carbides comprising a binder consisting of cobalt, nickel or iron, under certain sintering conditions and after the addition of specific additives to the hard component powder blends, a binder enriched layer which however is at the same time depleted in or free of solid solution carbides will form near the surfaces of the sintered cemented carbide bodies, while a binder depleted layer which however is at the same time enriched in solid solution carbides will form beneath the enriched layer.
As used herein, the term xe2x80x9ccermetxe2x80x9d refers to those materials, only, which comprise at least one metallic phase and at least one ceramic phase such as tungsten carbide (WC). Diamond and graphite per se are not considered to be xe2x80x9cceramicxe2x80x9d in the language of the present application. Thus, materials comprising diamond or graphite embedded in a metal matrix or bonded with a metal alloy do not form a xe2x80x9ccermetxe2x80x9d in the sense of the present invention.
It is the object of the present invention to provide a novel twist drill, and the like tools, having sintered cemented carbide bodies which comprise a binder consisting of cobalt, nickel and iron, but which, compared with presently available cermets having a binder comprising cobalt, nickel, and iron, exhibit improved mechanical properties, in particular an enhanced fatigue resistance and at the same time an enhanced toughness.
The invention teaches that this object can be achieved by a twist drill, comprising: a tip portion; a flute portion disposed adjacent to said tip portion; a central longitudinal axis; said tip portion being substantially cone shaped; said tip portion having a base portion and a top portion; said base portion being substantially wider than said top portion; said base portion being disposed immediately adjacent to said flute portion of said drill; said top portion being disposed on said tip portion opposite to said base portion; said tip portion comprising: a first chip face forming a portion of said conical surface of said tip portion; a second chip face forming a portion of said conical surface of said tip portion; a chisel edge arrangement configured to initiate drilling a material to be drilled; said chisel edge arrangement being disposed between said first chip face and said second chip face; said first chip face having a first end disposed adjacent to said chisel edge arrangement and a second end disposed opposite to said first end and adjacent to said body portion of said drill; said second chip face having a first end disposed adjacent to said chisel edge arrangement and a second end disposed opposite to said first end and adjacent to said body portion of said drill; said first chip face being configured to extend monotonically away from said flute portion to said chisel edge arrangement disposed on said top of said tip portion; said second chip face being configured to extend monotonically away from said flute portion to said chisel edge arrangement disposed on said top of said tip portion; said first chip face being disposed to meet said second chip face at said top of said tip portion; and said chisel edge arrangement comprising: a first chisel edge portion; a second chisel edge portion; each of said chisel edge portions being disposed to extend away from each other from said central longitudinal axis; wherein: at least a portion of said tip portion and at least a portion of said flute portion comprise a tool portion having an interior and an exterior; said tool portion comprising: a cermet body comprising at least one hard component and a binder, said binder comprising: in the range of from about forty weight percent to about ninety weight percent of cobalt; in the range of from about four weight percent to about thirty-six weight percent of nickel; in the range of from about four weight percent to about thirty-six weight percent of iron; and a ratio of nickel to iron in the range of from about one point five to one, to from about one to one point five; said binder in said body having a first concentration at a first portion and a second concentration at a second portion; said first concentration in said first portion being substantially different from said second concentration in said second portion to thus form a gradient in said body; said binder comprising a substantially face centered cubic structure; with the difference in concentration between said first concentration and said second concentration of said binder in said body being configured and disposed to substantially maintain said face centered cubic structure of said binder upon said binder being subjected to plastic deformation; and the difference in concentration between said first concentration and said second concentration of said binder in said body also being configured and disposed to minimize stress and strain induced transformations in said binder; and to maximize fatigue resistance and toughness in said body; and said flute portion comprising: a first chip flute; a second chip flute; and said first chip flute and said second chip flute being symmetric with respect to one another and substantially helically disposed about said central longitudinal axis; a first cutting edge, configured to drill, being disposed between said tip portion and said flute portion; a second cutting edge, configured to drill, being disposed between said tip portion and said flute portion; said first cutting edge and said second cutting edge being substantially symmetric with respect to one another about said central longitudinal axis; said first chip flute being disposed to extend helically along said flute portion from said first cutting edge; said second chip flute being disposed to extend helically along said flute portion from said second cutting edge; and said flute portion of said twist drill further comprising a shank portion configured of sufficient longitudinal extent to be positively secured in a chucking arrangement for a drill.
This object is also achieved in accordance with the invention in a sintered cemented carbide body of the initially defined species in that the concentration of the binder comprising cobalt, nickel, and iron has a gradient within the cemented carbide body and that the binder comprising cobalt, nickel, and iron has a face centered cubic structure and does not experience phase transformations induced by tension, strain or other stresses.
The concentration of the binder comprising nickel, cobalt, and iron preferably has a gradient which increases from the interior of the cemented carbide body toward the surfaces thereof. This gradient material, that is, in other words, the presence of a first concentration at a first portion and a second concentration at a second portion of the cermet, or gradient behavior of the binder comprising cobalt, nickel, and iron, is surprising to a person of ordinary skill in the art because it was unexpected that the three-component binder consisting of cobalt, nickel and iron, which preferably is present in the form of an alloy but does not necessarily have to be present as an alloy, would display a behavior similar to that of the cobalt binder frequently used in the past. Above all, it could not be expected that a distribution of the binder in the sintered cemented carbide as described above would result.
It is particularly advantageous if the binder comprising cobalt, nickel, and iron binder is enriched in a zone (xe2x80x9cbinder enriched zonexe2x80x9d, BEZ) near the surface of the cemented carbide body.
The binder enriched zone (BEZ) is preferably located at a depth of up to forty micrometers (xcexcm) as measured from the surface of the cemented carbide body.
In a preferred embodiment of the sintered cemented carbide body in accordance with the invention, the ratio of the constituents of the binder among each other, that is, cobalt-to-nickel-to-iron (Co:Ni:Fe), is the same within the enriched zone (BEZ) in the binder as that outside of the enriched zone (BEZ) in the binder. In this embodiment the diffusion of the binder into the enriched zone proceeds in a congruent manner, i.e. without a change in the composition of the binder. This, too, was surprising to a person of ordinary skill in the art because in complicated multi-component systems an incongruent behavior of the constituents of the binder alloy is the rule more often than not.
The binder comprising cobalt, nickel, and iron of the sintered cemented carbide body in accordance with the invention has a face centered cubic (fcc) structure and does not experience phase transformations induced by tension, strain or other stresses. The binder comprising cobalt, nickel, and iron is substantially austenitic.
Preferably, the proportion of the binder in the sintered cemented carbide amounts to four to ten weight percent.
The at least one hard component is preferably selected from the carbides, nitrides, carbonitrides, their mixtures, and their solid solutions, in any desired combination. Especially preferred hard components are the carbides of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten, as well as mixtures of a plurality of these carbides. Of the carbonitrides, those of titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, and tungsten, as well as their mixtures are preferred as hard components.
The sintered cemented carbide bodies in accordance with the invention are preferably used as cutting inserts, indexable inserts and for the production of cemented carbide tools and tool inserts of all kinds.
The above-discussed embodiments of the present invention will be described further hereinbelow. When the word xe2x80x9cinventionxe2x80x9d is used in this specification, the word xe2x80x9cinventionxe2x80x9d includes xe2x80x9cinventionsxe2x80x9d, that is the plural of xe2x80x9cinventionxe2x80x9d. By stating xe2x80x9cinventionxe2x80x9d, the Applicants do not in any way admit that the present application does not include more than one patentably and non-obviously distinct invention, and maintain that this application may include more than one patentably and non-obviously distinct invention. The Applicants hereby assert that the disclosure of this application may include more than one invention, and, in the event that there is more than one invention, that these inventions may be patentable and non-obvious one with respect to the other.